Effect of potassium on carbon adsorption on the Co(0001) surface.

The effect of potassium on carbon adsorption and deposition on the Co(0001) surface was studied on the basis of theoretical calculations. Thermodynamically, the surface C species is expected, and C dimer may be a critical elementary unit. With the increase of carbon coverage, a fraction of the carbon atoms may diffuse into the subsurface. But kinetically, the formation of C species is more favorable, and there is no driving force for carbon to migrate into the subsurface. As the surface carbon concentration increases, the adsorbed carbon atoms turn into carbon chains and then into graphene sheets parallel to the surface. Potassium promoter has little effect on the most stable adsorption configurations of carbon atoms but increases the adsorption energy of carbon species, which can be explained by the decreasing of the surface work function resulting from the electron effect of potassium promoter. The potassium promotes carbon deposition and carbonization of the cobalt surface to a certain extent. These results could support some useful information for the carbon deposition and cobalt carbide formation.